1. Field of the Invention
The invention relates to a method for comparing the quality of RF absorbers, in which a test absorber in a TEM cell which is provided with an absorber wall of reference absorbers, is irradiated with a steep-edged pulse wave and a scattered wave reflected from the test absorber is detected by means of a sensor.
2. Discussion of Background
Radio-frequency absorbers are very important in connection with EMI control. These absorbers are used, in particular, for creating anechoic test rooms.
To determine the properties of RF absorbers, mainly two methods are used, namely the arch method and the waveguide method. Both have the basic disadvantage that they are restricted to high frequencies (from approximately 100 MHz). In the arch method, the limitation is given by the size of the antenna and in the waveguide method it is given by the cut-off condition of the mode conducted or, respectively, the transverse dimension of the waveguide.
From the publication "An Investigation into the Scattering and Radiation Characteristics of RF-Absorbers", D. Hansen, N. Ari, H. Garbe, IEEE 1988 International Symposium on EMC, Seattle, USA, Aug. 2-4, 1988, a device is known by means of which the frequency response of RF absorbers can also be measured below 100 MHz. In this arrangement, a test absorber to be measured is introduced into a TEM cell used as test cell. This alone results in enormous advantages compared with the two usual methods. However, investigations have shown that the most recently known method does not fully exhaust the possibilities of the TEM cell.